Investigation of mechanical characteristics of materials based on refractory borides

Abstract

The object of research is the effect of sintering under pressure (10 MPa–4.1 GPa) on the formation of the structure and properties of ZrB 2 , HfB 2 , and composites on their bases. It has been found that high pressure consolidation results in an improvement of mechanical characteristics. In particular, the hardness and fracture toughness of the materials sintered under 4.1 GPa pressure are higher than those of the materials obtained under hot pressing conditions at 20–30 MPa and spark-plasma sintering at 50 MPa. High-pressure sintered HfB 2 demonstrated hardness H V (9.8 N)=21.3±0.8 GPa, H V (49 N)=19.3±1.3 GPa, and H V (98 N)=19.2±0.5 GPa and fracture toughness K 1C (49 N)=7.2 MPa · m 0.5 and K 1C (98 N)=5.7 MPa · m 0.5 . The HfB 2 sintered by hot pressing at 1850 °C and 30 MPa demonstrated hardness: H V (9.8 N)= 19.0 GPa , H V (49 N)= 18.7 GPa, and H V (98 N)=18.1 GPa, K 1C (9.8 N)=7.7 MPa · m 0.5 , K 1C (49 N)=6.6 MPa · m 0.5 and K 1C (98 N)=5.3 MPa · m 0.5 . High pressure sintered ZrB 2 (a=0.3167 nm, c=0.3528 nm, γ=6.2 g/cm 3 ) demonstrated H V (9.8 N)=17.7±0.6 GPa, H V (49 N)=15.4±1.2 GPa, and H V (98 N)=15.3±0.36 GPa and K 1C (9.8 N)=4.3 MPa · m 0.5 , K 1C (49 N)=4.2 MPa · m 0.5 and K 1C (98 N)=4.0 MPa · m 0.5 . Addition of 20 wt. % of SiC to ZrB 2 and sintering under high pressure (4.1 GPa) allowed essential increase of hardness to H V (9.8 N)=24.2±0.7 GPa, H V (49 N)=16.7±0.5 GPa, and H V (98 N)=17.6±0.4 GPa and fracture toughness to K 1C (49 N)=7.1 MPa · m 0.5 , K 1C (98 N)=6.2 MPa·m 0.5 ; the material density was γ=5.03 g/cm 3 . Additions of SiC and Si 3 N 4 to ZrB 2 lead to some increase in fracture toughness (up to K 1C (98 N)=9.2 MPa · m 0.5 ). The developed ZrB 2 - and HfB 2 -based materials and composites can be used for aerospace applications, in cutting and refractory industries, etc.